Packers are used downhole to isolate zones in a wellbore from each other. There are many styles currently in use. Some involve set down weight to mechanically compress the sealing element. Others use hydraulic pressure on a piston to compress the sealing element. Yet others use pressurized fluid to inflate an annular space between the mandrel and the sealing element to grow the sealing element radially as its length shortens.
Swelling rubbers have been a more recent development. These packers have to be shop fabricated because of specialized equipment needed to get a bonding relationship between the swelling rubber sleeve and the mandrel. Essentially, the packer assembly that is as long as a tubular section, with the rubber sleeve mounted to it has to be inserted into a long oven and heated to obtain the desired bond to the mandrel. This process is expensive and requires the maintaining of a large inventory of different sizes at remote locations.
Packers that are field assembled have been used in the past. These designs involved a slip on of a tubular shaped cylindrical assembly that had two layers of natural and non-swelling rubber that were separated by a Mylar® sheet to define an inflatable annular space between the layers. Tubing would be connected to the annular space to deliver the inflation fluid. To keep the element from shifting, a hinged clamp was made up over the tubular and disposed at opposed ends of the slipped on element assembly. There were many problems with this design that date back to the 1970s. Apart from issues of over inflation leading to a rupture of the element assembly, the clamps proved unreliable. The vibration in a tubular string that is inherent to its use downhole made the bolted connections on the clamp release. Apart from that, the clamps were damaged during run in by striking the wellbore. The design was discontinued.
Ring structures have been formed in place for tubulars to serve as centralizers for such purposes as to keep the tubular centralized for cementing in deviated wells.
What is needed and provided by the present invention is a packer design that can be field assembled using, preferably, an element assembly that swells downhole to create a seal. It is retained to the mandrel by rings that are formed to the tubular so that variations in the outer dimensions of the tubular become unimportant. The assembly can further feature different swelling materials to protect the ends of the main swelling material during run in. These and other aspects of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawing that appear below, while recognizing that the full scope of the invention is to be found in the claims.